We require the design of a 6 cell Lithium Ion Polymer balanced battery charger and monitor. The battery would typically be a 19.8 volt, 1 amp hour pack of high discharge capability (40C+). The battery charger shall have the following features:
• Accept a 5 volt USB input. This input must respect the USB loading limits for the different classes of USB charge source.
• Accept a 24 volt input for the purpose of providing a 1 hour charge.
• Provide over-charge protection.
• Provide over-discharge protection.
• Provide charge current regulation.
• Provide Battery Short Circuit Protection.
• Provide a balanced charge and discharge such that each cell in the pack is never over charged or discharged.
• Be designed with EMC compatibility in mind.
• Be designed with a low component count.
• Have low to insignificant shutdown drain current to prevent battery under-voltage when stored for a significant length of time.
The battery balancing must use a modern integrated device to minimise the total component count. This balancing device may be of a passive (energy dumping) or active design. A microcontroller will be utilised to establish communication between devices. A boost convertor shall elevate the USB voltage of 5 volts to a level suitable for charge purposes.
An initial design has been produced which is to be developed and improved upon. The design process will be iterative with periodic review. You will not be expected to work in isolation.
The successful candidate should have formal engineering qualifications, industrial experience, and familiarity with switched mode systems and embedded software development.
The work will be split into several stages as follows:
1. Detailed review of the initial design. Does our initial design meet our requirements? You will be expected to analyse and appraise the initial design. This will involve research of potentially more suitable devices on the market, a study of the overall methodology, looking particularly at performance, anticipated reliability, with regard to component count and costs.
2. Design a development circuit board layout for development purposes. Route the board(s) in suitable CAD software and get the board(s) manufactured. These boards will then require component placement and solder reflow. It is likely that many packages will only be available in fine pitch surface mount.
3. Debugging of the hardware. The board will require careful debugging looking for correct function throughout. The use of a current limited supply and oscilloscope would be essential.
4. Detailed performance analysis of the boost convertor. This must be verified as meeting the given performance requirements. All components must be verified to be working within manufacturer limits. The convertor must be demonstrated to operate in a stable manner without significant voltage ringing at any point.
5. Detailed performance analysis of the charger. Analysis requirements will be as for the boost convertor.
6. Detailed performance analysis of battery balancer. It is highly likely that in order to perform this task communication with a microcontroller will be necessary. Analysis requirements will be as for the boost convertor.
7. Development of microcontroller software to implement all servicing requirements of relevant hardware. This could include the development of a battery balancing algorithm.
It is not a requirement that the candidate should be able to manufacture and reflow the board(s). This can be completed elsewhere. Owing to the nature of development work it is not possible to accurately predict the time taken to reasonably complete each listed stage. Remuneration will be negotiated in advance of each stage. All work will remain the intellectual property of the Whey Forward Health Industries Ltd.